Detailed introduction to regular expressions in python

This article brings you a detailed introduction to regular expressions in python. It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

Regular

re = regular experssion
re module enables the Python language to have all the regular expression functions.
The compile function generates a regular expression object based on a pattern string and optional flag parameters. This object has a series of methods for regular expression matching and replacement.

Function: When processing a string, it will check whether the content of the string matches the regular expression you wrote.

If it matches, take out the matching content;
If it does not match, ignore it. Matching content;

Writing regular rules

pattern matching regular expression
string string to be matched

Three search methods

1). findall

import re

str = 'hello sheen,hello cute.'

pattern_1 = r'hello'
pattern_2 = r'sheen'
print(re.findall(pattern_1,str))    #['hello', 'hello']
print(re.findall(pattern_2,str))    #['sheen']

2).match

match attempts to match from the starting position of the string,

• If the starting position is not matched successfully, a None is returned;

• If the starting position is matched successfully, an object will be returned;

import re

str = 'hello sheen,hello cute.'

pattern_1 = r'hello'
pattern_2 = r'sheen'
print(re.match(pattern_1,str))           #<_sre.sre_match>
print(re.match(pattern_1,str).group())   #返回match匹配的字符串内容,hello
print(re.match(pattern_2,str))           #None</_sre.sre_match>

3).search

search will scan the entire string and only return the first successfully matched content;

• If it can be found, return an object and obtain the corresponding string through the group method;

import re

str = 'hello sheen,hello cute.'

pattern_1 = r'hello'
pattern_2 = r'sheen'
print(re.search(pattern_1,str))             #<_sre.sre_match>
print(re.search(pattern_1,str).group())     #hello
print(re.search(pattern_2,str))             #<_sre.sre_match>
print(re.search(pattern_2,str).group())     #sheen</_sre.sre_match></_sre.sre_match>

Special character class

.: Matches any character except \n; [.\n]
\d: digit--(number), matches a numeric character, equivalent to [0-9]
\ D: Matches a non-numeric character, equivalent to [^0-9]
\s: space (generalized space: space, \t, \n, \r), matches any single whitespace character;
\S: Matches any whitespace character except a single one;
\w: Alphanumeric or underscore, [a-zA-Z0-9_]
\W: Except alphanumeric or underscore, [^a-zA- Z0-9_]

import re

# .
print(re.findall(r'.','sheen\nstar\n'))     #['s', 'h', 'e', 'e', 'n', 's', 't', 'a', 'r']

#\d#\D
print(re.findall(r'\d','当前声望30'))       #['3', '0']
print(re.findall(r'\D','当前声望30'))       #['当', '前', '声', '望']

#\s#\S
print(re.findall(r'\s', '\n当前\r声望\t为30'))     #['\n', '\r', '\t']
print(re.findall(r'\S', '\n当前\r声望\t为30'))     #['当', '前', '声', '望', '为', '3', '0']

#\w#\W
print(re.findall(r'\w','lucky超可爱!!'))           #['l', 'u', 'c', 'k', 'y', '超', '可', '爱']
print(re.findall(r'\W','lucky超可爱!!'))           #['!', '!']

Specify the number of occurrences of characters

The number of occurrences of matching characters:

*: represents the previous character appearing 0 times or infinite times; d*, .*
: represents the previous character appearing once or infinite times; d
?: represents the previous character appearing 1 time or 0 times; Assuming that some characters can be omitted, you can also use

when not omitting. The second method:

{m}: The previous character appears m times;
{m, }: The previous character appears at least m times; * == {0,}; ==={1,}
{m,n}: The previous character appears m to n times; ? === {0 ,1}

import re

#* 代表前一个字符出现0次或者无限次
print(re.findall(r's*','sheenstar'))        #['s', '', '', '', '', 's', '', '', '', '']
print(re.findall(r's*','hello'))            #['', '', '', '', '', '']

#+ 代表前一个字符出现一次或者无限次
print(re.findall(r's+','sheenstar'))        #['s', 's']
print(re.findall(r's+','hello'))            #[]

# ？ 代表前一个字符出现1次或者0次
print(re.findall(r'188-?', '188 6543'))     #['188']
print(re.findall(r'188-?', '188-6543'))     #['188-']
print(re.findall(r'188-?', '148-6543'))     #[]


# 匹配电话号码
pattern = r'\d{3}[\s-]?\d{4}[\s-]?\d{4}'
print(re.findall(pattern,'188 0123 4567'))      #['188 0123 4567']
print(re.findall(pattern,'188-0123-4567'))      #['188-0123-4567']
print(re.findall(pattern,'18801234567'))        #['188-0123-4567']

Exercise--Matching IP

You can search for a regular expression generator from the Internet, use the rules written by others, and test it yourself.

import re

# | 表示或者
pattern = r'(25[0-5]|2[0-4]\d|[0-1]\d{2}|[1-9]?\d)\.(25[0-5]|2[0-4]\d|[0-1]\d{2}|[1-9]?\d)\.(25[0-5]|2[0-4]\d|[0-1]\d{2}|[1-9]?\d)\.(25[0-5]|2[0-4]\d|[0-1]\d{2}|[1-9]?\d)$'

print(re.findall(pattern,'172.25.254.34'))  #[('172', '25', '254', '34')]

matchObj_1 = re.match(pattern,'172.25.254.34')
if matchObj_1:
    print('匹配项：',matchObj_1.group())                     #172.25.254.34
else:
    print('未找到匹配项')

matchObj_2 = re.match(pattern,'172.25.254.343')
if matchObj_2:
    print('匹配项：',matchObj_2.group())                     
else:
    print('未找到匹配项')

The above is the detailed content of Detailed introduction to regular expressions in python. For more information, please follow other related articles on the PHP Chinese website!